“Tip-of-the-Tongue” Phenomenon in Parkinson’s Disease: A Hidden Gem

Persons with Parkinson’s disease (PD) often experience impairments in verbal language expression and other communication tasks such as handwriting and keyboarding. With respect to speech, its execution can be impaired by decreased volume and hypokinetic dysarthria.¹ Spoken language also can be disrupted by intermittent silences in between otherwise fluent speech. This episodic event has been euphemistically designated as the “tip-of-the-tongue” (TOT) phenomenon. Those experiencing TOT phenomena characterize it as a transient difficulty at finding the right word. This recurrent interruption of speech is especially annoying because the speaker has a distinct notion of what was intended to be said. TOT is analogous to another intermittent problem some PD patients experience, motor blocks of gait (freezing), although the two phenomena are independent of one another. In today’s PD clinics, TOT phenomenon is a commonly reported experience (PAL, personal observation) though it has received little attention since 1982, when Matison and colleagues reported this topic to the neurology community.²

In their prospective study of 22 cognitively-intact PD patients, Matison and colleagues observed prominent word-finding difficulties (which they termed TOT phenomena) during testing that involved visual confrontation naming, Further investigation revealed that these PD patients achieved only partial knowledge of words. From the neuropsychological assessments, Matison and colleagues concluded that the distinctive impairment of spoken language they observed in PD was the TOT phenomenon, readily differentiated from hypokinetic dysarthria or other problems of motor execution. Previous research into the experience of TOT phenomena led other investigators to characterize it as failure at recalling a previously known word, usually happening when the feeling of recall seemed imminent.³ Further investigation has revealed that the TOT phenomenon can be a universal experience, occurring independently of PD or other neurological disorders and at any age. Some of its properties include recognition of only the first letter of a target word, or recall that is directed at semantically related words.⁴ One common example of TOT phenomena would be the halted naming of a widely-known person.⁵

In other studies, the TOT state was investigated in healthy controls and in individuals with various forms of aphasia. For example, patients with conduction aphasia were more adept at indicating both the first letter and the number of syllables in a forgotten word, compared with patients affected by either Wernicke aphasia or anomic aphasia.⁶ In some instances, individuals displaying fluent aphasia could recover a word without ability to provide answers that would indicate their partial knowledge about the word. While individuals with conduction aphasia generally retain the normal neural process of recall, this ability seems to be impaired at connecting to articulatory movements needed for word production. In one study of this phenomenon, all subjects were able to select the correct word provided in multiple choice format, confirming that TOT phenomena are primarily problems of recall rather than for recognition of words.⁶ Recent metacognitive research posits that the mental annoyance of TOT occurrences may serve to stimulate the mind into a “need-to-know” state.⁷

Beyond the daily problem of episodic paused speech, the TOT phenomenon may be a window into functioning of neural circuitry in disorders like PD. The distinctive episodic interruption of spoken language production, as reported by Matison and colleagues,² provided the first published recognition of TOT phenomenon and important insights into yet another non-motor manifestation of PD.⁸ Further research is warranted to investigate the effect of TOT stimulus tasks that might improve word finding skills in PD and in other neurological conditions. A broad research study comparing verbal fluency and tip of the tongue occurrences in non-fluent aphasia and people with PD would be the next step in such a project.

Since the TOT phenomenon has also been reported to occur in healthy controls as well as those with neurological disorders, it may represent part of the normal aging process.⁹ Reports reveal that older adults often cite TOT as being a common and troubling memory and cognitive problem particularly involving proper names. In some cases, an alternative or “interloper” word comes to mind before the target word, further interfering with the intended word recall.^9,10 The cognitive interference of the TOT phenomenon may then create pauses in conversation and interrupt verbal fluency and the pragmatics of discourse. Based on these reports, TOT appears to represent higher level cognitive interruptions in healthy controls as well as those with neurological disorders. Further research is necessary to understand why TOT occurs and to differentiate normal interruptions in word recall from those of disordered language and cognition. Results of such research may improve treatment options in individuals with TOT in the future.